Opencart how to test if vqmod installed?

I have written a module that uses vqmod for opencart. How can I check if vqmod is installed from within the admin module?

I would like to display a warning inside of the module that checks if vqmod is installed? Even better would be to check if it also has correct write permission to generate cached files and write to the vamod.log

What is the best way of doing this?

PS: it would be cool if you could tag questions with vqmod. I dont have enough reputation to create a new tag.

<?php
    if(class_exists('VQMod')) {
         // vqmod exists
    }
?>